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/*=========================================================================
Program: Insight Segmentation & Registration Toolkit
Module: $RCSfile: itkOtsuThresholdImageCalculator.txx,v $
Language: C++
Date: $Date: 2006-03-28 23:46:10 $
Version: $Revision: 1.8 $
Copyright (c) Insight Software Consortium. All rights reserved.
See ITKCopyright.txt or http://www.itk.org/HTML/Copyright.htm for details.
This software is distributed WITHOUT ANY WARRANTY; without even
the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE. See the above copyright notices for more information.
=========================================================================*/
#ifndef _itkOtsuThresholdImageCalculator_txx
#define _itkOtsuThresholdImageCalculator_txx
#include "itkOtsuThresholdImageCalculator.h"
#include "itkImageRegionConstIteratorWithIndex.h"
#include "itkMinimumMaximumImageCalculator.h"
#include "vnl/vnl_math.h"
namespace itk
{
/*
* Constructor
*/
template<class TInputImage>
OtsuThresholdImageCalculator<TInputImage>
::OtsuThresholdImageCalculator()
{
m_Image = NULL;
m_Threshold = NumericTraits<PixelType>::Zero;
m_NumberOfHistogramBins = 128;
m_RegionSetByUser = false;
}
/*
* Compute the Otsu's threshold
*/
template<class TInputImage>
void
OtsuThresholdImageCalculator<TInputImage>
::Compute(void)
{
unsigned int j;
if ( !m_Image ) { return; }
if( !m_RegionSetByUser )
{
m_Region = m_Image->GetRequestedRegion();
}
double totalPixels = (double) m_Region.GetNumberOfPixels();
if ( totalPixels == 0 ) { return; }
// compute image max and min
typedef MinimumMaximumImageCalculator<TInputImage> RangeCalculator;
typename RangeCalculator::Pointer rangeCalculator = RangeCalculator::New();
rangeCalculator->SetImage( m_Image );
rangeCalculator->Compute();
PixelType imageMin = rangeCalculator->GetMinimum();
PixelType imageMax = rangeCalculator->GetMaximum();
if ( imageMin >= imageMax )
{
m_Threshold = imageMin;
return;
}
// create a histogram
std::vector<double> relativeFrequency;
relativeFrequency.resize( m_NumberOfHistogramBins );
for ( j = 0; j < m_NumberOfHistogramBins; j++ )
{
relativeFrequency[j] = 0.0;
}
double binMultiplier = (double) m_NumberOfHistogramBins /
(double) ( imageMax - imageMin );
typedef ImageRegionConstIteratorWithIndex<TInputImage> Iterator;
Iterator iter( m_Image, m_Region );
while ( !iter.IsAtEnd() )
{
unsigned int binNumber;
PixelType value = iter.Get();
if ( value == imageMin )
{
binNumber = 0;
}
else
{
binNumber = (unsigned int) vcl_ceil((value - imageMin) * binMultiplier ) - 1;
if ( binNumber == m_NumberOfHistogramBins ) // in case of rounding errors
{
binNumber -= 1;
}
}
relativeFrequency[binNumber] += 1.0;
++iter;
}
// normalize the frequencies
double totalMean = 0.0;
for ( j = 0; j < m_NumberOfHistogramBins; j++ )
{
relativeFrequency[j] /= totalPixels;
totalMean += (j+1) * relativeFrequency[j];
}
// compute Otsu's threshold by maximizing the between-class
// variance
double freqLeft = relativeFrequency[0];
double meanLeft = 1.0;
double meanRight = ( totalMean - freqLeft ) / ( 1.0 - freqLeft );
double maxVarBetween = freqLeft * ( 1.0 - freqLeft ) *
vnl_math_sqr( meanLeft - meanRight );
int maxBinNumber = 0;
double freqLeftOld = freqLeft;
double meanLeftOld = meanLeft;
for ( j = 1; j < m_NumberOfHistogramBins; j++ )
{
freqLeft += relativeFrequency[j];
meanLeft = ( meanLeftOld * freqLeftOld +
(j+1) * relativeFrequency[j] ) / freqLeft;
if (freqLeft == 1.0)
{
meanRight = 0.0;
}
else
{
meanRight = ( totalMean - meanLeft * freqLeft ) /
( 1.0 - freqLeft );
}
double varBetween = freqLeft * ( 1.0 - freqLeft ) *
vnl_math_sqr( meanLeft - meanRight );
if ( varBetween > maxVarBetween )
{
maxVarBetween = varBetween;
maxBinNumber = j;
}
// cache old values
freqLeftOld = freqLeft;
meanLeftOld = meanLeft;
}
m_Threshold = static_cast<PixelType>( imageMin +
( maxBinNumber + 1 ) / binMultiplier );
}
template<class TInputImage>
void
OtsuThresholdImageCalculator<TInputImage>
::SetRegion( const RegionType & region )
{
m_Region = region;
m_RegionSetByUser = true;
}
template<class TInputImage>
void
OtsuThresholdImageCalculator<TInputImage>
::PrintSelf( std::ostream& os, Indent indent ) const
{
Superclass::PrintSelf(os,indent);
os << indent << "Threshold: " << m_Threshold << std::endl;
os << indent << "NumberOfHistogramBins: " << m_NumberOfHistogramBins << std::endl;
os << indent << "Image: " << m_Image.GetPointer() << std::endl;
}
} // end namespace itk
#endif
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